Does anyone know where I can find a track planning software for the Apple Macintosh, preferably one that is either OS X or OS 9 compatable?
It will be much easier (and likely) for you to find a Windows-compatible track planning program, and run it on your Mac using a "virtual PC" environment like SoftWindows or VirtualPC or whatever is OSX compatible.
As a Mac owner myself, I find that often this is the only way to find niche-market software, since the Mac market is so small that it is very difficult for a niche-market software company to profitably make a Mac version.